/*-------------------------------------------------------------------------
 *
 * tupdesc_details.h
 *	  POSTGRES 元组描述符定义，无法随处包含
 *
 *
 * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/tupdesc_details.h
 *
 *-------------------------------------------------------------------------
 */

#ifndef TUPDESC_DETAILS_H
#define TUPDESC_DETAILS_H


/*
 * 结构用于表示在元组中完全不存在时使用的值，即列在元组创建后才被创建
 */
typedef struct AttrMissing
{
	bool		am_present;		/* 如果存在非 NULL 的缺失值则为真 */
	Datum		am_value;		/* 当属性缺失时的值 */
} AttrMissing;

#endif							/* TUPDESC_DETAILS_H */
